Azimuth is an angular measurement in a spherical coordinate system. The vector from an observer (origin) to a point of interest is projected perpendicularly onto a reference plane; the angle between the projected vector and a reference vector on the reference plane is called the azimuth. A position of a star in the sky can be measured using this concept. In such an example, the reference plane is the horizon or the surface of the sea beneath the point of interest being measured (i.e. the star), and the reference vector points to the north. The azimuth is then the angle between the north vector and the perpendicular projection of the star down onto the horizon. Azimuth is usually measured in degrees (°) and the reference plane for an azimuth in a general navigational context is typically true north, measured as a 0° azimuth. For example, moving clockwise on a 360 degree circle, a point due east would have an azimuth of 90°, south 180°, and west 270°.
The concept may be used in many practical applications including navigation, astronomy, engineering, mapping, mining and artillery. Present hand held azimuth determination (i.e. compassing) devices and methods rely on magnetic sensors to determine azimuth.
Some known devices and techniques for determining azimuth utilise data provided by an inertial measurement unit (IMU). An IMU comprises three accelerometers and three gyroscopes and optionally three magnetometers. The accelerometers are placed such that their measuring axes are orthogonal to each other. They measure inertial acceleration, also known as G-forces. Three gyroscopes are placed in a similar orthogonal pattern, measuring rotational position in reference to an arbitrarily chosen coordinate system. The accelerometers and gyroscopes therefore produce inertial data and in known azimuth determination devices, a processor would normally process the inertial data from the IMU, via strapdown and inertial navigation algorithms, to derive a navigation solution. Other known devices for determining azimuth use GPS systems. Some known handheld devices use magnetic sensors to determine azimuth.